Malaria continues to cause incomprehensible human suffering throughout most of the tropics and subtropics: in sub-Saharan Africa it is estimated that 2 million children die each year as a direct cause of
infection with Plasmodium. Vector control and
malaria chemotherapy that were previously effective in controlling and treating
malaria are now largely ineffective due to
insecticide-resistant mosquitoes and
drug-resistant parasites. As alternatives to these mainstays of control, an intensive effort to develop
subunit vaccines targeted at various stages of the life has been undertaken. One such
vaccine, directed against the sexual and sporogonic stages and referred to as a transmission-blocking
vaccine, offers the hope of controlling
malaria in geographically isolated areas, preventing re-introduction of the parasite in
malaria-free zones, blocking the spread of
drug-resistant or
vaccine escape mutants, and reducing exposure to "virulent" strains of parasites. A series of potential transmission-blocking
vaccine candidates have identified and the genes encoding these
surface proteins have now been isolated and sequenced. One such
vaccine candidate, Pfs25, is now being tested in human Phase I safety and immunogenicity studies. Here the use and status of transmission-blocking
vaccines are reviewed.